The application of heavy, high viscosity fuel oils requires their pre-treatment involving the heating of the fuel up to a certain temperature so as to decrease the viscosity of the heavy fuel down to that of the light, or diesel fuel.
There is known a single loop device for supplying fuel to a diesel engine (cf. P. P. Botkin, V. A. Somov "Application of Heavy Fuel Oils in Marine Diesel Engines", Sudpromgis, 1959, p. 111) comprising a heavy fuel tank and a diesel oil tank, the tanks being alternately connected via a three-way cock to a loop supplying fuel to a diesel engine, the diesel engine incorporating a fuel priming pump, a fuel heater and a filter.
However, as light and heavy fuels enter the device alternately and pass along the same pipes, a failure of any of the components necessitates stoppage of the diesel engine for repairs.
Besides, a large amount of fuel in the device makes it impossible to effect a rapid change-over from one kind of fuel to the other, the replacement of one kind of fuel with the other taking place gradually, as the fuel is burnt in the diesel engine.
Furthermore, it is impossible to effect the pre-heating of heavy fuel in the device when the engine operates on light fuel, as in this case the heavy fuel should be heated in the tank up to the working temperature which may result in an ignition thereof.
As heavy fuel shouldn't be kept in the tank at working temperature, automatic change-over from one kind of fuel to the other cannot be effected.
There is also known a device (cf P. P. Botkin, V. A. Somov, "Application of Heavy Fuel Oils in Marine Diesel Engines", Sudpromgis, 1959, pp. 112, 113) comprising a light fuel loop and a heavy fuel loop, the loops being alternately connected to a diesel engine via a system of stop valves. Each loop comprises a fuel tank, a fuel priming pump, a filter and interconnecting piping. Two fuel pre-treatment loops make it possible to pre-heat heavy fuel while the engine works on light fuel.
The delivery of the pre-heated heavy fuel to fuel injection pumps and injectors results in a greater wear of said device caused by a temperature difference of the fuel and the fuel injection system sometimes causing scuffing and jamming of precision pairs of the fuel injection apparatus, i.e. a failure thereof.
Therefore the change-over from the light fuel to the heavy fuel is effected with some time delay enabling fuel injection pumps and fuel injectors to be warmed to a temperature near that of the heavy fuel. In this period the diesel engine receives a mixture of heavy and light fuels, the amount of the heavy fuel in the mixture increasing with the fuel injection apparatus getting more warmed up.
However, a large number of stop valves (six, at least) which are to be switched over to the opposite direction when changing the fuel delivered to the priming pipe affects the reliability of the device, the control thereof being more complicated because of sealing of the stop valves and leakage of the heated heavy fuel likely to occur therethrough.
Also known in the art is a fuel supply device for a diesel engine, described in the USSR Inventor's Certificate No. 619686 comprising alternately connected to a diesel engine a light fuel loop and a heavy fuel loop incorporating a tank and a fuel priming pump, the loops being in communication with a suction pipe of fuel injection pumps of the diesel engine via a system of stop valves. Besides, the light fuel loop additionally communicates with the diesel engine for cooling fuel injectors and warming fuel injection pumps thereof.
The device comprises two independent loops, circulation of fuel through pipes in each loop being possible without mixing fuel flows. The loops are in communication with the suction pipe of fuel injection pumps of the engine via six stop valve units. Besides, the light fuel loop is used for preheating the light fuel by passing it through cooling cavities of fuel injectors thus providing gradual warming-up of the fuel equipment by heat removed from fuel injectors in case of cold start of the engine on light fuel. Simultaneously the heavy fuel circulating through its loop is heated by a special purpose heater. A temperature level of both fuels is monitored by a special automatic device, an order for the diesel engine change-over to the heavy fuel being formed at the appropriate instant.
However, the above device is rendered unreliable due to a large number of stop valves, each having two positions: open and closed. To actuate the units each of them should be provided with a drive supplied with a control signal to bring it into one of said positions. Moreover, each stop valve has a stem linking the drive with a closing element of the stop valve unit. These stems should be sealed to avoid leakage of the fuel passing through the stop valve units. Each of said units decreases the reliability of the device as a whole, since damage of one of the units will disturb the normal operation of the device this arising from mixing of the fuels, which can result in an emergency situation.